Stator of outer rotor type motor for drum type washer

ABSTRACT

The present invention provides an outer rotor type motor for a drum type washing machine to reduce material and weight for fabrication, simplify fabrication process, provide stable assembly of a stator to a fixing side such as a tub or a bearing housing, prevent by assembly interference caused by a difference in the tips in assembling the upper and lower insulators the stator and enhancing loading efficiency of a cylindrical sleeve provided to inner circumference of fastening holes of the upper and lower insulators. The present invention includes a helical core having multiple layers formed by winding steel plates in a helix, the steel plate having a base portion with teeth projected from the base portion, an upper and lower insulators of an electric insulating material covered on upper and lower sides of the helical core in shapes complementary to shapes of the helical core, respectively, and at least three fastening portions formed as one body in each of the upper and lower insulators and projected from an inside of the helical core toward a center of the stator, wherein a boss forming a fastening hole for securing the stator to a tub wall with fastening members is provided, wherein a ridge portion, projected toward the confronting insulator, is provided to a vicinity of the boss, and wherein the ridge portions are pressed closely together in assembling the upper and lower insulators.

This application claims the benefit of the Korean Application No.P2004-13267 filed on Feb. 27, 2004 and P2004-12999 filed on Feb. 26,2004 which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drum type washing machine, and moreparticularly, to a stator of an outer rotor type BLDC motor, which isapplicable to a direct coupling type drum type washing machine.

2. Discussion of the Related Art

Generally, a drum type washing machine performs washing operation withthe aid of a drive force of a motor which spins a drum containinglaundry, detergent, and water, to cause friction between laundry andwater. The drum type washing machine causes almost no damage to thelaundry, prevents tangling of the laundry, and brings about the effectsof pounding and rubbing.

Drum type washing machines are categorized by an indirect coupling typeand a direct coupling type according to a drive system. In the indirectcoupling type, a drive force of a motor is indirectly transferred to adrum via a motor pulley and a belt wound to the drum pulley. In thedirect coupling type, a rotor of a BLDC motor is directly coupled with adrum to directly transfer a drive force to the drum.

Yet, in the indirect coupling type system that transfers the drive forceof the motor to the drum via the motor pulley and the belt wound on thedrum pulley instead of transferring the drive force of the motor to thedrum directly, energy loss occurs in the process of drive force transferand considerable noise is generated.

Hence, the direct coupling drum type washing machine using the BLDCmotor is widely used to solve the above problems of the drum typewashing machine.

FIG. 1 is a cross-sectional diagram of a direct coupling drum typewashing machine according to a related art.

Referring to FIG. 1, a tub 2 is provided within a cabinet 1, and a drum3 is rotatably provided within the tub 2.

A motor is provided to a rear portion of the tub 2. Specifically, astator 6 is fixed to a rear wall of the tub 2 and a rotor 5 encloses thestator 6 to be coupled to the drum 3 via a shaft.

A door 21 is provided to a front portion of the cabinet 1 and a gasketis provided between the door 21 and the tub 2.

A hanging spring 23 supporting the tub 2 is provided between an insideof a top portion of the cabinet 1 and an upper outer circumference ofthe tub 2, and a friction damper 24 is provided between an inside of abottom portion of the cabinet 1 and a lower outer circumference of thetub 2 to attenuate vibration of the tub 2.

FIG. 2 is a perspective diagram of a stator in FIG. 1 and FIG. 3 is aperspective diagram of a sectional core (SC) applied to the stator inFIG. 2.

A method of manufacturing a stator core according to a related art isexplained as follows.

First of all, a plurality of unit cores are fabricated by a pressingprocess of a steel plate. In doing so, each of the unit cores consistsof teeth 151, a base 150, and a protrusion 500 opposite to the teeth 151for forming a fastening hole 500 a. A plurality of the unit cores arestacked to form a plurality of assemblies. And, a plurality of theassemblies are linked in a circumferential direction to complete astator core that is so-called a stator core.

The protrusion 500 plays a role in standing a fastening force of a boltas well as provides the fastening hole 500 a necessary for securing astator to the rear wall of the tub.

Yet, such a method of manufacturing the stator 6 with the sectional coreSC is very complicated and brings about considerable loss of materials.

Meanwhile, a helical core, which is manufactured by helically stacking asteel plate consisting of teeth 151 and a base 150, is very useful inreducing the loss of materials and simplifying the manufacturingprocess. Yet, in manufacturing the helical core HC, the steel plateblanked like a strap needs to be helically bent. Hence, it is unable toprovide a protrusion for coupling a stator with a tub to an inside ofthe core.

If the protrusion 500 is provided to the inside of the core inmanufacturing the helical core HC, a core width of a part reserved forthe protrusion is too large to bend the core.

Accordingly, a stator structure that enables the same role of theprotrusion of the sectional core to be performed not by the core itselfbut by another portion is needed to be applicable to the helical coreHC.

Meanwhile, it is important to sufficiently secure the rigidity of theprotrusion provided with the fastening hole for securing the stator tothe tub, which is explained as follows.

First of all, in a washing machine that rotates a drum directly using aBLDC motor, a stator is directly assembled to a fixing side of a rearportion of the tub. If the stator of a motor for a high capacity drumtype washing machine weighs over 1.5 kg and if a dewatering rotationalspeed is 600˜2,000 RPM, a fastening portion of the stator 6 is brokendue to the stator weight, the vibration of the high rotation, and theshake and transformation of the rotor 5.

Specifically, in case that the stator is coupled with the rear wall ofthe tub of the drum type washing machine using the BLDC motor, a radialdirection of the stator almost maintains parallel to a ground, thebreakage of the fastening portion of the stator 6 to the rear wall ofthe tub gets worsened due to the vibration occurring on driving thewashing machine.

Therefore, it is important to sufficiently secure the rigidity of theprotrusion provided with the fastening hole for securing the stator 6 tothe tub.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a stator of an outerrotor type motor for a drum type washing machine that substantiallyobviate one or more problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide an outer rotor typemotor for a drum type washing machine, by which a material and weightfor fabrication are reduced, by which a fabrication process issimplified, and by which a stator can be stably assembled to a fixingside such as a tub or a bearing housing.

Another object of the present invention is to provide a stator of anouter rotor type motor for a drum type washing machine, in which astator can be stably assembled to a fixing side such as a tub or abearing housing and by which the stator weighing at least 1.5 kg isapplicable to a drum type washing machine BLDC motor having a rotationalspeed over 2,000 RPM.

A further object of the present invention is to provide a stator, bywhich an assembly interference caused by a difference in the tips inassembling the upper and lower insulators of the stator is prevented andby which loading efficiency of a cylindrical sleeve provided to innercircumference of fastening holes of the upper and lower insulators isenhanced.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, astator of an outer rotor type motor for a drum type washing machineaccording to the present invention includes a helical core havingmultiple layers formed by winding steel plates in a helix starting froma bottom layer to a top layer, the steel plate having a base portionwith teeth projected from the base portion, an upper insulator of anelectric insulating material covered on an upper side of the helicalcore in a shape complementary to a shape of the helical core, a lowerinsulator of an electric insulating material covered on a lower side ofthe helical core at the time of assembly with the upper insulator havinga shape complementary to a shape of a helical core, and at least threefastening portions formed as one body in each of the upper and lowerinsulators and projected from an inside of the helical core toward acenter of the stator for fastening the stator to a fixing side of a tub,wherein a boss forming a fastening hole for securing the stator to a tubwall with fastening members is provided, wherein a ridge portion,projected toward the confronting insulator, is provided to a vicinity ofthe boss on each assembled side of the upper and lower insulators, andwherein the ridge portions are pressed closely together in assemblingthe upper and lower insulators to enhance assembly efficiency of theupper and lower insulators.

In another aspect of the present invention, a stator of an outer rotortype motor for a drum type washing machine comprises a helical corehaving multiple layers formed by winding steel plates in a helixstarting from a bottom layer to a top layer, the steel plate having abase portion with teeth projected from the base portion, an upperinsulator of an electric insulating material covered on an upper side ofthe helical core in a shape complementary to a shape of the helicalcore, a lower insulator of an electric insulating material covered on alower side of the helical core at the time of assembly with the upperinsulator having a shape complementary to a shape of a stator core, atleast three fastening portions formed as one body in each of the upperand lower insulators and projected which projects from an inside of thehelical core toward a center of the stator for fastening the stator to afixing side of a tub, wherein a boss forming a fastening hole forsecuring the stator to a tub wall with fastening members is provided,and wherein at least one fastening projection is provided at an innercircumference of the fastening hole of the boss to prevent a separationof a cylindrical sleeve in the fastening hole.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a cross-sectional diagram of a direct coupling drum typewashing machine according to a related art;

FIG. 2 is a perspective diagram of a stator in FIG. 1;

FIG. 3 is a perspective diagram of a sectional core (SC) applied to thestator in FIG. 2;

FIG. 4 is a perspective diagram of a stator according to the presentinvention;

FIG. 5 is a projected perspective diagram of the stator in FIG. 4;

FIG. 6 is a perspective diagram of a backside of an upper insulator inFIG. 5;

FIG. 7 is a layout of the stator in FIG. 4;

FIG. 8A and FIG. 8B are front diagrams of an insulator for common use;and

FIG. 9 is a layout of a fastening member of a stator according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Embodiments of the present invention are explained with reference toFIGS. 4 to 9 as follows.

First of all, one embodiment of the present invention is explained withreference to FIGS. 4 to 6 as follows.

FIG. 4 is a perspective diagram of a stator according to the presentinvention, FIG. 5 is a projected perspective diagram of the stator inFIG. 4, and FIG. 6 is a perspective diagram of a backside of an upperinsulator in FIG. 5.

Referring to FIGS. 4 to 6, a stator 6 of an outer rotor type motoraccording to one embodiment of the present invention comprises a helicalcore HC having multiple layers formed by winding steel plates in a helixstarting from a bottom layer to a top layer, the steel plate having abase portion 150 with teeth 151 projected from the base portion 150, anupper insulator 60 a of an electric insulating material covered on anupper side of the helical core HC in a shape complementary to a shape ofthe helical core HC, a lower insulator 60 b of an electric insulatingmaterial covered on a lower side of the helical core HC at the time ofassembly with the upper insulator 60 a having a shape complementary to ashape of a helical core HC, and at least three fastening portions 600formed as one body in each of the upper and lower insulators 60 a and 60b and projected from an inside of the helical core HC toward a center ofthe stator 6 for fastening the stator 6 to a fixing side of a tub.

A fastening portion 600, as shown in FIG. 5, has a fastening hole 620 afor securing the stator 6 to a fixing side, such as a tub, with afastening member. The fastening hole 620 a is formed by a boss 620projected to the back side of the fastening portion 600.

Furthermore, ridges 621 are provided to a vicinity of the bosses 620 oneach assembled side of the upper and lower insulators 60 a and 60 b andare projected toward the confronting insulator, respectively. The ridges621 are pressed closely together in assembling the upper and lowerinsulators 60 a and 60 b, thereby enhancing assembly efficiency of theupper and lower insulators 60 a and 60 b.

A support rib 650 is provided on an inside along a circumferentialdirection thereof in contact with the helical core for supporting aninside surface of the helical core HC in each of the upper insulator 60a and lower insulator 60 b.

Furthermore, the fastening portion 600 of each of the upper insulator 60a and the lower insulator 60 b includes at least one reinforcing rib 660connected between the boss 620 of the fastening hole 620 a and thesupporting rib 650 for spreading fastening force concentrated on theboss 620 and reinforcing a strength of the fastening portion 600.

As shown in FIG. 7, the fastening portion 600 of each of the upperinsulator 60 a and the lower insulator 60 b has a reinforcing rib 670 atan inside circumference thereof, and at least one connection rib 680connected between the reinforcing rib 670 and the supporting rib 650which supports an inside surface of the core in a radial direction, forproviding a supporting force.

Each of the upper insulator 60 a and the lower insulator 60 b has tips610 a on opposite sidewalls of each of the teeth 610 thereof havingshapes in complementary to each other for fitting in at the time ofassembly to form a flush surface.

In this case, if one of the tips 610 a and 610 b has a ‘┐’ shape, theother has a ‘└’ shape.

At the opposite end surfaces substantially perpendicular to the oppositesidewall surfaces of the teeth 610 of the upper insulator 60 a and thelower insulator 60 b, there are tips 610 a and 610 b having shapes incomplementary to each other. Hence, the further-provided tips 610 a and610 b engage with each other in assembling the upper and lowerinsulators 60 a and 60 b.

The teeth 610 of each of the upper insulator 60 a and the lowerinsulator 60 b has a seating surface 611 a at an end for seating a coreshoe 151 a of the helical core HC.

Along with this, in the vicinity of the fastening hole 620 a of thefastening portion 600 of the upper insulator 60 a, there is apositioning projection 630 having a shape in complementary to apositioning hole or a slot (not shown) in the fixing side of the tub.

Moreover, there is a cylindrical sleeve 800 in the fastening hole 620 a,a spring pin having an elasticity owing to an incised portion, or ahollow pin enabling press fit in the fastening hole 620 a, serves as abushing.

A plurality of recesses 152 are provided to the base portion 150 of thehelical core HC to facilitate a winding work for core formation byreducing stress. Moreover, the helical core HC is fastened by rivets 153passed through pass through holes in the base portion 150.

A winding beginning portion or a bottom layer of the helical core HC anda winding end portion or a top layer of the helical core HC can bewelded to predetermined contact portions of the base portion 150.

Referring to FIG. 7, the stator 6 according to the present inventionincludes at least three fastening portions 600 formed as one body ineach of the upper insulator 60 a and the lower insulator 60 b whichprojects from an inside of the helical core toward a center of thestator for fastening the stator to a fixing side of a tub.

If a length of each of the teeth 151 projected from a lateral outside ofthe helical core HC is set to ‘a’ and if a distance from a lateralinside of the helical core to a center of the fastening hole of thefastening portion 600 is set to ‘b’, the fastening portion 600 is formedto meet a definition of ‘a≧b’.

Meanwhile, a reference number ‘8’ in FIG. 5 indicates a hole sensorassembly for a motor control and a reference number ‘9’ indicates a taphousing assembly for power connection to supply power to the statorside.

An operation of the above-configured present invention is explained asfollows.

First of all, the helical core, which is formed in a manner of helicallyrotating to stack the steel plate including the teeth 151 and the base150, is used as the core 15 configuring the stator. Hence, the presentinvention does not need the processes of assembling and welding unitcores for the sectional core, thereby simplifying the fabricatingprocess.

And, the helical core HC according to the present invention has not theprotrusions of the sectional core, thereby reducing the material loss.

Namely, the method of fabricating the stator according to the presentinvention is simple and reduces the material loss.

Moreover, the ridges 621 are provided to vicinities of the bosses 620 atassembled sides of the upper and lower insulators 60 a and 60 b and areprojected toward the confronting insulator, respectively. The upper andlower insulators 60 a and 60 b are assembled to each other by contactingthe ridges 621 of the boss side of the upper insulator 60 a with thoseof the lower insulator 60, respectively, whereby assembly efficiency ofthe upper and lower insulators 60 a and 60 b is enhanced.

Namely, if the ridges 621 are not provided, by a height difference,i.e., difference in the tips, between the tips 610 a or 610 b providedto an outer circumference of the upper or lower insulator 60 a or 60 band a surface of the corresponding boss 620 provided to an innercircumference of the upper or lower insulator 60 a or 60 b, the tips 610a and 610 initially come into contact with each other in assembling theupper and lower insulators 60 a and 60 b. Hence, the upper or lowerinsulators 60 a and 60 b are assembled together while the bosses 620 ofthe upper and lower insulators 60 a and 60 b are separated from eachother.

Thus, the assembly is carried out without the contact between the bosses620 of the upper and lower insulators 60 a and 60 b. Hence,transformation due to the bending or distortion may occur in the area ofthe upper or lower insulator 60 a or 60 b provided with the bosses 620in case that a shock, vibration, or the like is applied to the assembledupper insulator 60 a and/or the lower insulator 60 b.

To overcome such a problem, the ridges 621 are provided to thevicinities of the bosses 620 to enable the assembly of the upper andlower insulators 60 a and 60 b by making the confronting ridges 621press closely to each other. Hence, the assembly efficiency of theassembled sides of the upper and lower insulators 60 a and 60 b can beenhanced to prevent the transformations of the upper and lowerinsulators 60 a and 60 b which are caused by the difference in the tips.

Moreover, the stator 6 of the present invention has sufficient rigidityagainst the fastening force of the bolt in a manner of improving thestructure of the upper and lower insulators 60 a and 60 b withoutforming the protrusion for standing the fastening force in fixing thestator 6 to the core itself.

That is, by providing structures that work the same with the projectedportion of the division core to the fastening portions 600 of the upperinsulator 60 a and the lower insulator 60 b, a stator 6 can be provided,to which the helical core HC is applicable.

Moreover, spaces 640 between the ribs 650, 660, 670, and 680 at a backside of the fastening portion 600 dampen and attenuate vibrationoccurred during driving the motor, to improve mechanical reliability ofthe stator 6, and contributes to the reduction of the insulatormaterial.

The supporting ribs 650 of the upper insulator 60 a and the lowerinsulator 60 b formed at an inside in contact with the helical core HCalong the circumferential direction support an inside of the helicalcore HC.

The reinforcing rib 660 connected between the boss 620 of the fasteninghole 620 a and the supporting rib 650 at each of the fastening portion600 of the upper insulator 60 a and the lower insulator 60 b spread thefastening force concentrated on the boss 620, and reinforces a strengthof the fastening portion 600.

According to this, the stator 6 can effectively prevent a fasteningportion of the stator 6 suffering from breakage caused by vibration atthe spinning, shaking and deformation of the rotor 5 even at a largecapacity drum type washing machine having a weight over 1.5 kg only ofthe stator, and a spinning speed ranging 600˜2,000 RPM.

As a positioning projection 630 in the vicinity of the fastening hole620 a of the fastening portion 600 fits in a positioning hole (notshown) in the tub 2, fastening of the stator is easy.

Hence, the location setting projection 630 facilitates the stator 6according to the present invention to be coupled with the tub 2, wherebya maintenance and repair work of a serviceman can be easily done forafter-service.

Alternatively, it is a matter of course that the positioning projection630 may be formed on the tub 2, and the positioning hole may be formedin the fastening portion 600.

FIG. 8A and FIG. 8B are reference drawings, illustrating a versatilityof application of the insulators, wherein it can be noted that the upperand lower insulators 60 a and 60 b, respectively, are applicable even ifa total height of the helical core varies within a certain range.

FIG. 8A, a stacked height h1 of the core corresponds to a height in casethat the stepped portions 610 a and 610 b of the upper and lowerinsulators 60 a and 60 b completely engage with each other.

That is, FIG. 8 a illustrates a case when a total height h1 of the coreis a height which permits tips 610 a and 610 b of the upper and lowerinsulators 60 a and 60 b fit exactly. FIG. 9 b illustrates a case when atotal height of the core is a height greater than a case of FIG. 9 asuch that the tips 610 a and 610 b of the upper and lower insulators 60a and 60 b are unable to fit exactly, but spaced a certain distance.

Even if the total height h2 of the core is greater than a height thatpermits the tips 610 a and 610 b of the upper and lower insulators 60 aand 60 b, respectively, fit exactly, such that there is a space betweenthe tips 610 a and 610 b, because the insulation against the core teethis still achievable; the upper and lower insulators 60 a and 60 b areapplicable to the case of FIG. 8 b, too.

Thus, since the separate type upper and lower insulators of theembodiment are applicable to the core regardless of the total height ofthe core within a certain range of the total height, the separate typeupper and lower type insulators of the embodiment can improveworkability on an assembly line.

FIG. 9 is a layout of a fastening portion of a stator according toanother embodiment of the present invention.

Referring to FIG. 9, a fastening portion of a stator according toanother embodiment of the present invention has the same configurationof that of the stator according to the former embodiment of the presentinvention except but differs only in having at least one fasteningprojection 620 b provided at an inner circumference of the fasteninghole of the boss to prevent a separation of the cylindrical sleeve 800in the fastening hole.

Namely, to prevent the separation of the cylindrical sleeve 800installed in the fastening hole 620 a, the fastening projection 620 b isprovided to the inner circumference of the fastening hole 620 a.

Preferably, a plurality of the fastening projections 620 b are providedat the inner circumference of the fastening hole 620 a along acircumferential direction.

Moreover, a length of the fastening projection 620 b is set equal to orsmaller than a depth of the fastening hole 620 a of the boss 620 a.

Preferably, a cross-section of the fastening projection 620 b issemicircular in shape. Yet, the cross-section of the fasteningprojection 620 b may be oval or can be variously modified.

An operation of another embodiment of the present invention is explainedas follows.

First of all, the present embodiment basically has the same operation ofthe former embodiment but differs in having the following operation ofthe fastening projection 620 b.

Namely, the fastening projection 620 b, which is provided to thefastening hole 620 a of each of the upper and lower insulators 60 a and60 b, pressurizes an outer circumference of the cylindrical sleeve 800inserted in the fastening hole 620 a, thereby preventing the cylindricalsleeve 800 from escaping from the fastening hole 620 a.

Therefore, a secure assembly of the cylindrical sleeve can be achieved.

Accordingly, the present invention provides the following effects oradvantages.

First of all, the material and weight for fabrication of the stator ofthe BLDC motor for the drum type washing machine are reduced, thefabrication process is simplified, and the stator can be stablyassembled to the fixing side such as a tub.

Specifically, the stator can be stably assembled to the fixing side suchas a tub or a bearing housing like the case of applying the sectionalcore, whereby the stator weighing at least 1.5 kg is applicable to adrum type washing machine BLDC motor having a rotational speed over2,000 RPM.

Secondly, the stator is facilitated to be assembled to the tub, wherebya maintenance and repair work of a serviceman can be easily done forafter-service.

Thirdly, the present invention enhances the assembly efficiency of theupper and lower insulators to raise the rigidity of the stator, therebyenhancing the mechanical reliability and endurance by reducing the noiseand vibration.

Finally, by installing the cylindrical sleeve playing a role of thebushing in the fastening hole of upper or lower insulator securely, thepresent invention raises the rigidity of the stator to reduce the noiseand vibration thereof, thereby enhancing the mechanical reliability andendurance.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A stator of an outer rotor motor for a drum washing machine, comprising: a core having multiple layers, the core having a base portion with teeth projecting from the base portion; an upper insulator of an electric insulating material covering an upper side of the core in a shape complementary to a shape of the core; a lower insulator of an electric insulating material covering a lower side of the core in a shape complementary to the shape of the core; and a plurality of fastening portions formed at each of the upper and lower insulators projecting from an inner side of each of the upper and lower insulators the core toward a center of the stator for fastening the stator to a tub, each of the plurality of the fastening portions including a boss having a ridge, wherein the boss has a fastening hole for securing the stator to a tub wall with fastening members, and extends toward a confronting insulator from each of the fastening portions, wherein the ridge projects toward the confronting insulator from the boss, and wherein the confronting ridges are in contact with each other.
 2. The stator of claim 1, wherein each of the upper insulator and the lower insulator includes a supporting rib on an inside along a circumferential direction thereof in contact with the core for supporting an inside surface of the core.
 3. The stator of claim 2, wherein the fastening portion of each of the upper insulator and the lower insulator includes at least one reinforcing rib connected between the boss of the fastening hole and the supporting rib for spreading fastening force concentrated on the boss and reinforcing a strength of the fastening portion.
 4. The stator of claim 1, wherein each of the upper insulator and the lower insulator includes tips on opposite sidewalls of each of the teeth thereof having shapes in complementary to each other for fitting in at the time of assembly to form a flush surface.
 5. The stator of claim 4, wherein the tips on opposite sidewalls of each of the teeth include ‘└’ shape if the other side of the upper, and lower insulators includes a ‘┐’ shape.
 6. The stator of claim 1, further comprising tips having shape in complementary to each other at opposite end surfaces substantially perpendicular to opposite sidewall surfaces of the teeth of the upper insulator and the lower insulator.
 7. The stator of claim 1, wherein each of the teeth of the upper insulator and the lower insulator includes a seating surface at an end for seating a core shoe of the core.
 8. The stator of claim 1, wherein the insulator includes a positioning projection in the vicinity of the fastening hole thereof having a shape in complementary to a positioning hole or a slot on the tub.
 9. The stator of claim 1, further comprising a cylindrical sleeve on an inside of the fastening hole.
 10. The stator of claim 9, wherein the cylindrical sleeve is a spring pin having elasticity owing to a portion incised along a length direction of an outside surface.
 11. The stator of claim 9, wherein the cylindrical sleeve is a hollow pin press fit in the fastening hole, the cylindrical sleeve having no incised portion.
 12. The stator of claim 1, wherein the base portion of the core includes slots for reducing stress during winding the core.
 13. The stator of claim 1, wherein the multiple layers are fastened by rivets passed through pass through holes in the base portion.
 14. The stator of claim 1, wherein the bottom layer and the top layer of the core are welded to predetermined portions of the base portion, respectively.
 15. The stator of claim 1, wherein if a length of each of the teeth projected from a lateral outside of the core is set to ‘a’ and if a distance from a lateral inside of the core to a center of a fastening hole of a fastening portion is set to ‘b’, ‘a’ is equal to or greater than ‘b’ (a≧b).
 16. A stator of an outer rotor motor for a drum washing machine, comprising: a core having multiple layers, the core having a base portion with teeth projecting from the base portion; an upper insulator of an electric insulating material covering an upper side of the core in a shape complementary to a shape of the core; a lower insulator of an electric insulating material covering a lower side of the core in a shape complementary to the shape of the core; and a plurality of fastening portions formed at each of the upper and lower insulators projecting from an inner side of each of the upper and lower insulators toward a center of the stator for fastening the stator to a tub, each of the plurality of the fastening portions including a boss having a ridge and at least one fastening projection, wherein the boss has a fastening hole for securing the stator to a tub wall with fastening members, and extends toward a confronting insulator from each of the fastening portions, wherein the at least one fastening projection is formed on an inner circumferential surface of the boss to prevent a separation of a cylindrical sleeve in the fastening hole.
 17. The stator of claim 16, wherein a plurality of the fastening projections are provided on an inside along a circumferential direction of the fastening hole at predetermined distances from each other.
 18. The stator of claim 16, wherein a projected shape of each of the at least one fastening projections has a hemispherical shape.
 19. The stator of claim 16, wherein each of the upper insulator and the lower insulator includes a supporting rib on an inside along a circumferential direction thereof in contact with the core for supporting an inside surface of the core.
 20. The stator of claim 19, wherein the fastening portion of each of the upper insulator and the lower insulator includes at least one reinforcing rib connected between the boss of the fastening hole and the supporting rib for spreading fastening force concentrated on the boss and reinforcing a strength of the fastening portion.
 21. The stator of claim 16, wherein each of the upper insulator and the lower insulator includes tips on opposite sidewalls of each of the teeth thereof having shapes in complementary to each other for fitting in at the time of assembly to form a flush surface.
 22. The stator of claim 21, wherein the tips on opposite sidewalls of each of the teeth include ‘└’ shape if the other side of the upper, and lower insulators includes a ‘┐’ shape.
 23. The stator of claim 16, further comprising tips having shape in complementary to each other at opposite end surfaces substantially perpendicular to opposite sidewall surfaces of the teeth of the upper insulator and the lower insulator.
 24. The stator of claim 16, wherein each of the teeth of the upper insulator and the lower insulator includes a seating surface at an end for seating a core shoe of the core.
 25. The stator of claim 16, wherein the insulator includes a positioning projection in the vicinity of the fastening hole thereof having a shape in complementary to a positioning hole or a slot on the tub.
 26. The stator of claim 16, wherein the cylindrical sleeve is a spring pin having elasticity owing to a portion incised along a length direction of an outside surface.
 27. The stator of claim 16, wherein the cylindrical sleeve is a hollow pin press fit in the fastening hole, the cylindrical sleeve having no incised portion.
 28. The stator of claim 16, wherein at least one recess is provided to the base of the core to reduce stress in winding the core.
 29. The stator of claim 16, wherein the multiple layers are fastened by rivets passed through pass through holes in the base portion.
 30. The stator of claim 16, wherein the bottom layer and the top layer of the core are welded to predetermined portions of the base portion, respectively.
 31. The stator of claim 16, wherein if a length of each of the teeth projected from a lateral outside of the core is set to ‘a’ and if a distance from a lateral inside of the core to a center of a fastening hole of a fastening portion is set to ‘b’, ‘a’ is equal to or greater than ‘b’ (a≧b).
 32. A stator of an outer rotor motor for a drum washing machine, comprising: a core having multiple layers, the core having a base portion with teeth projecting from the base portion; an upper insulator of an electric insulating material covering an upper side of the core in a shape complementary to a shape of the core; a lower insulator of an electric insulating material covering a lower side of the core in a shape complementary to the shape of the core; and a plurality of fastening portions formed at each of the upper and lower insulators projecting from an inner side of each of the upper and lower insulators toward a center of the stator for fastening the stator to a tub, each of the plurality of the fastening portions including a boss having a ridge and at least one fastening projection, wherein the boss has a fastening hole for securing the stator to a tub wall with fastening members is provided to the fastening portion, and extends toward a confronting insulator from each of the fastening portions, wherein the ridge projects toward the confronting insulator from the boss, wherein the confronting ridges are in contact with each other, and wherein the at least one fastening projection is formed on an inner circumferential surface of the boss to prevent a separation of a cylindrical sleeve in the fastening hole.
 33. The stator of claim 32, wherein each of the upper insulator and the lower insulator includes a supporting rib on an inside along a circumferential direction thereof in contact with the core for supporting an inside surface of the core.
 34. The stator of claim 33, wherein the fastening portion of each of the upper insulator and the lower insulator includes at least one reinforcing rib connected between the boss of the fastening hole and the supporting rib for spreading fastening force concentrated on the boss and reinforcing a strength of the fastening portion.
 35. The stator of claim 32, wherein each of the upper insulator and the lower insulator includes tips on opposite sidewalls of each of the teeth thereof having shapes in complementary to each other for fitting in at the time of assembly to form a flush surface.
 36. The stator of claim 35, wherein the tips on opposite sidewalls of each of the teeth include ‘└’ shape if the other side of the upper, and lower insulators includes a ‘┐’ shape.
 37. The stator of claim 32, wherein a plurality of the fastening projections are provided on an inside along a circumferential direction of the fastening hole at predetermined distances from each other.
 38. The stator of claim 37, wherein a projected shape of each of the at least one fastening projections has a hemispherical shape.
 39. The stator of claim 37, wherein a length of each of the at least one fastening projection is equal to or smaller than a depth of the fastening hole of the corresponding boss.
 40. The stator of claim 1, wherein the core is a helical core.
 41. The stator of claim 16, wherein the core is a helical core.
 42. The stator of claim 32, wherein the core is a helical core.
 43. The stator of claim 1, wherein the stator is fastened to the tub only by the plurality of the fastening portions.
 44. The stator of claim 16, wherein the stator is fastened to the tub only by the plurality of the fastening portions.
 45. The stator of claim 32, wherein the stator is fastened to the tub only by the plurality of the fastening portions.
 46. The stator of claim 16, wherein the at least one fastening projection pushes the cylindrical sleeve in a radial direction to prevent the cylindrical sleeve from escaping out of the fastening hole.
 47. The stator of claim 32, wherein the at least one fastening projection pushes the cylindrical sleeve in a radial direction to prevent the cylindrical sleeve from escaping out of the fastening hole. 